Hitherto, in a construction machine and the like, an axial type hydraulic piston pump which is driven by an engine or an axial type hydraulic piston motor which is driven by pressure oil has been frequently used.
For example, the axial type hydraulic piston pump includes a cylinder block which is provided so as to rotate along with a rotation shaft rotatably provided inside a casing and is provided with a plurality of cylinders spaced from each other in the circumferential direction and extending in the axial direction, a plurality of pistons which are slidably inserted and fitted into the respective cylinders of the cylinder block and move in the axial direction with the rotation of the cylinder block so as to suction and discharge hydraulic oil, and a valve plate which is provided between the casing and an end surface of the cylinder block and is provided with a suction port and an ejection port communicating with the respective cylinders. Then, in the hydraulic pump, when a drive shaft is rotationally driven, the cylinder block rotates inside the casing along with an operation shaft, pistons reciprocate inside the respective cylinders of the cylinder block, and the hydraulic oil suctioned from the suction port into the cylinder is pressurized by the piston, whereby the hydraulic oil is discharged as pressure oil in the ejection port.
Here, when the cylinder port of each cylinder communicates with the suction port of the valve plate, the piston moves in a direction protruding from the cylinder from the start end of the suction port to the terminal end thereof and an intake operation is performed in which the hydraulic oil is suctioned from the suction port into the cylinder. On the other hand, when the cylinder port of each cylinder communicates with the ejection port, the piston moves in a direction entering the cylinder from the start end of the ejection port to the terminal end thereof and a delivery operation is performed in which the hydraulic oil inside the cylinder is discharged into the ejection port. Then, when the cylinder block rotates so as to repeat the suction operation and the delivery operation, the hydraulic oil which is suctioned into the cylinder from the suction port by the suction operation is pressurized by the delivery operation so as to be ejected in the ejection port.